General synthesis and atomic arrangement identification of ordered Bi–Pd intermetallics with tunable electrocatalytic CO2 reduction selectivity

Intermetallic compounds (IMCs) with fixed chemical composition and ordered crystallographic arrangement are highly desirable platforms for elucidating the precise correlation between structures and performances in catalysis. However, diffusing a metal atom into a lattice of another metal to form a controllably regular metal occupancy remains a huge challenge. Herein, we develop a general and tractable solvothermal method to synthesize the Bi-Pd IMCs family, including Bi2Pd, BiPd, Bi3Pd5, Bi2Pd5, Bi3Pd8 and BiPd3. By employing electrocatalytic CO2 reduction as a model reaction, we deeply elucidated the interplay between Bi-Pd IMCs and key intermediates. Specific surface atomic arrangements endow Bi-Pd IMCs different relative surface binding affinities and adsorption configuration for *OCHO, *COOH and *H intermediate, thus exhibiting substantially selective generation of formate (Bi2Pd), CO (BiPd3) and H2 (Bi2Pd5). This work provides a comprehensive understanding of the specific structure-performance correlation of IMCs, which serves as a valuable paradigm for precisely modulating catalyst material structures.

corresponding Supplementary Figures S17 and S18 only indicate the transition state energy barrier but do not indicate the thermodynamic energy barrier for this step of the reaction.Moreover, in Figure S17a, it appears that the energy barrier for * OCHO to * HCOOH is actually higher, which is inconsistent with the textual description; And there is a syntax error in "While the different absorption configurations change the subsequence reaction paths for separate products."3.At line 441，Did you increase kpoints when calculating DOS？ Suggest explanation for this.

Dear reviewers,
We would like to thank you for the prompt and thorough review of our manuscript.These comments are valuable and greatly help in the improvement of the manuscript.We have carefully studied the comments, supplemented the experiments and provided a substantive discussion of the results.Please find our point-by-point responses to the reviewer's comments below and the corresponding revisions in red text in the revised manuscript.

For reviewer #1:
The authors developed a solvothermal method to tune the atomic-level surface structure and the compositional stoichiometry of Bi-Pd IMCs, which were well characterized.The interplay between Bi-Pd intermetallics and the key intermediates of electrocatalytic CO2 reduction has been investigated by the density functional theory calculations and in-situ Fourier-transform infrared spectroscopy.Below are my specific comments for major revision.After the authors could provide all necessary studies to support their conclusions, we might further consider the publication.
Comments 1) Six Bi-Pd IMCs samples shown in Figure 1d have large differences in particle size and morphology, which could significantly affect their CO2RR performance rather than surface atomic arrangements.Please verify this by additional experiments.

Our response:
We thank for the reviewer's extremely insightful comments.It is well known that particle size and morphology might have great influences on catalytic performance.In this work, all the Bi-Pd IMCs display irregular grain-like morphologies, and the particle size of most Bi-Pd IMCs is in the range of 75-100 nm, while obvious size difference exists among S1, S4 and S6 samples.According to the reviewer's suggestion, we synthesized a series of different sized Bi-Pd IMCs to study the size effect on electrocatalytic behavior.
The particle sizes of Bi2Pd (S1), Bi2Pd5 (S4) and BiPd3 (S6) IMCs were regulated by varying the content of surfactant PVP during synthesis process, and the experimental details have been added to the Supplementary Information in the revised version.As shown in following Figure R1a-R3a, the XRD diffraction peaks of different samples are in good agreement with the standard patterns of Bi2Pd, Bi2Pd5 and BiPd3 IMCs, respectively.Figures R1b-R3b show the SEM images and the corresponding size distribution of each IMCs with the same stoichiometry but different sizes.For Bi2Pd, the particle size varies from 100 to 200 nm, while a slight current density fluctuation and an almost unchanged formate selectivity were observed toward electrocatalytic CO2RR (Figure R1c~d).When we switch to the Bi2Pd5 sample with relatively large crystal sizes, as shown in Figure R2c~d, different sized Bi2Pd5 samples demonstrate negligible activity variations from two perspectives of H2 FE and constant potential (-0.7 V vs. RHE) electrolysis, even their size difference is hundreds of nanometers.Interestingly, the similar phenomenon also take place on the BiPd3 samples with relatively small sizes (Figure R3c~d).These results indicate that the particle size has a negligible effect on CO2RR performance.
In addition, we also carefully compare the activity of Bi2Pd and BiPd3 IMCs with similar particle size (Figure R4), which reveals dramatically different activity and selectivity.The Bi2Pd and BiPd3 performs catalytic selectivity toward formate and CO, respectively.Besides, Bi2Pd shows a larger current density than BiPd3.These results also prove that the surface atomic arrangement rather than the particle size of Bi

Comments 2)
The authors need to explain why they performed the constant potential electrolysis at -0.7V while evaluated the stability at -1 V?
Our response: We appreciate for the reviewer's preciseness.In fact, we indeed studied constant potential electrolysis at -0.7 V (see graph legend in Fig 4h).However, we mismarked the potential as -1 V in the figure caption.We are very sorry for our carelessness and have corrected it in the revised manuscript (highlighted with red color in the revised version).
Comments 3) In Figure 4b, the current densities of samples S4, S5 and S6 increase after a long reaction time, while current densities of other samples decrease with the increase in reaction time.Authors are encouraged to explain this.

Our response:
We thanks a lot for this extremely insightful comment.In fact, as shown in Figure 4b, the current fluctuations of the samples were actually slight during the constant potential electrolysis.However, with the gradual extension of the reaction time, the current density of the samples will inevitably fluctuate with different degrees.The variation trend of current densities between different samples proposed by reviewers is present and also very interesting.Nevertheless, it is not easy to fully understand the trend of the total current density of this reaction.Therefore, we try to analyze the possible reasons of this difference from the following perspectives: (1) In our flow-cell system, the gaseous product is in a state of continuous flow, while the liquid product is in the enriched.As the reaction time increases, the accumulation of products inevitably impacts the reaction equilibrium.Consequently, as the reaction proceeds, the activity of generating the liquid product will present a more pronounced decrease compared to that of the gaseous product flowing in the gas chamber.
(2) The results from both DFT calculation and activity experiments indicate that the HER activity of samples S1, S2 and S3 is comparatively lower than that of samples S4, S5 and S6.
It suggests that HER serves as a more competitive side reaction for the samples of S4, S5 and S6.Therefore, with an increase in reaction time, the enhancement in HER activity will be more pronounced for samples S4, S5, and S6 compared to the other three samples.
(3) The reduction ability of the adsorbed CO2 gradually decreases as reaction time prolongs for the six synthesized Bi-Pd IMCs, while the activity of the HER gradually increases.Both factors contribute to the total current density of the reaction.Among these samples, S5 and S6 exhibit higher CO production and fewer liquid products.Consequently, there is no significant decrease in the current density of CO2RR, but a notable increase in the current density of the strong side reaction HER, resulting in a slight overall increase in total current density.In contrast, for samples S1 and S2, formate is predominantly produced along with minimal gas phase production of CO.As a result, there is a more pronounced decrease in the current density of CO2RR while weak side reactions HER do not significantly increase.Therefore, there is a slight decrease in total current density for these samples.Additionally, for the samples S3 and S4, there are no noticeable differences between gaseous and liquid product selectivity.Thus, changes in the side reactions HER play key roles in variations observed during electrolysis time prolongation on total current density.Specifically for sample S3, the decline in product activity nearly equals an increase in side reaction HER activity, therefore, no change is observed in the total current density over time during electrolysis.However, in case of sample S4, the increased activity of dominant HER leads to an overall increase in total current density (Figure 4b).

Comments 4)
The authors should give infrared data within a wider wavenumber range, and assign other peaks in the infrared spectrum that vary with the potential, such as the variation of peaks around 1240 cm -1 in the infrared spectrum of S6 as shown in Figure 5e.

Our response:
We thank for the reviewer's useful comment.According to the reviewer's suggestion, we have provided the FT-infrared full spectra of S1, S4 and S6 in the range of 1000-4000 cm -1 in the revised supplementary information (Fig. S30 in the revised version).As shown in the full spectra below (Figure R5-R7), the prominent peak observed around 3000-3600 cm -1 can be attributed to the stretching vibration peak of water molecules.Additionally, the signals at 2200-2400 cm -1 may be with CO2 stretching vibrations.To minimize interference from strong water and carbon dioxide signals, our focus lies on comparing signal differences within the range of 1000-2000 cm -1 in the IR spectra, as shown in Figure 5e

Comments 5)
The authors used anion exchange membranes to test the performance of CO2RR, so it is necessary to explain how to avoid the carbon loss caused by the crossover of formate and bicarbonate during the long-term test.A closed carbon mass balance accounting for all carbon should be provided to assure that the results are valid (determination of gaseous CO2 at the cathode and anode outlet, of organic molecules in the gas phase in the catholyte as well as anolyte, and of carbonate in the catholyte and anolyte necessary).

0V
Our response: We thank for the reviewer's useful comment and totally agree with the reviewer's opinion.Typically, the anion exchange membrane is used when gaseous products dominate CO2 reduction, while the proton exchange membrane is employed for liquid product formation.In this study, different proportions of liquid and gas products were generated over various Bi-Pd IMCs.However, it should be noted that using a proton exchange membrane may lead to a significant decrease in pH caused by OER on the anode side, which negatively affect CO2RR activity on the cathode side (Figure R8a~b).This concern was further verified through a comparative experiment with both types of membranes (Figure R8c).Therefore, we utilized anion exchange membrane in this work.At the same time, we addressed concerns raised by reviewers regarding crossover of liquid phase products and carbon loss by providing the following experiments to assure that our results are valid.
We thoroughly analyzed carbon balance from both perspectives of cathode and anode sides.
Firstly, we measured the formate content in the catholyte, anolyte and anode-cathode mixture of S1 and S6 after constant potential electrolysis by using ion chromatograph (Figure R9), respectively.As shown in Figure R10, regardless of the amount of produced formate, only trace amounts of formate (4-6% of catholyte) were detected in the anolyte.This indicates that crossover behavior is negligible and can be avoided by measuring the mixed electrolyte.
Subsequently, to address the carbon loss phenomenon in the alkaline conditions, carbonate concentrations were determined in both the anode and cathode compartments of S1 and S6.
Based on CO2 input and detected carbonate levels, a rough mass balance accounting for carbon within the reaction system was conducted (Table R1).As expected, there was minimal presence of carbonate in the electrolyte after reaction completion (~0.8-1% carbon loss), suggesting that such losses are likely insignificant.It may be probably owing to the unique three-phase reaction interface in the flow-cell, avoiding the contact loss of CO2 with the alkaline electrolyte.

Table R1|
Carbon mass balance calculation of S1 and S6.

For reviewer #2:
In this paper, the authors reported preparation of a set of BiPd intermetallic catalysts by solvothermal method, by selecting the amount or the type of Pd salt precursors.The author performed detailed examination for the as prepared catalysts by Aberration corrected TEM and XAFS and DFT calculation and in-situ FTIR were also performed for the catalysts, which is really impressive.There are several reports about the synthesis and application of BiPd intermetallic, which are equally prepared by hydrothermal method, but using different solvent and metal precursors.The concept of the paper, nor the findings seem very new.Thus, the authors may need to highlight the novelty and broad impact of this work.Comments 3) Currently, the production of formate is already not very exciting for electrochemical CO2RR.The selectivity and current density for C2 products productions can be up to 80% and 1-2 A cm -2 .-S6).      as the Pd precursor obtained at various reaction times.

Comments 5)
The clarity of the figures provides is quite low and need to be improved.

Our response: We thank for the reviewer's useful comment. According to the suggestion of the reviewer, the clarity of all the figures provided in the manuscript has been improved and we have replaced all the figures in the original version as requested. (highlighted in the red color in the revised version)
For reviewer #3: The DFT calculation section of the article provides detailed research on HER and CO2RR reactions occurring on S1, S4, and S6, but there are still several issues: Comments 1) The content of Supplementary Fig. S18 at line 236 does not correspond to the HER reaction described in the text.

Our response:
We thank for the reviewer's preciseness.We are very sorry for our misspelling of graphic Numbers."Fig.S18" should be Fig.S16b  Comments 3) At line 441，Did you increase kpoints when calculating DOS？ Suggest explanation for this.

Our response:
We thank for the reviewer's useful comment.In the catalytic process, our focus lies predominantly on the electronic state of the material and the shift in the D-band center of the active atom.However, we keep K-points consistent for catalytic process and DOS calculations by using the same number of K-points.This is primarily due to the utilization of a cut-off surface rather than its unit structure form in DOS calculations, resulting in a significantly larger system and an exponential increase in computational requirements with additional K-points.For our current system, K-points of 2*2*1 and 3*3*1 adequately suffice for accurate DOS calculations.
The revised version has already been submitted online.
Thank you for your consideration!

REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author): Authors prepared intermetallic BiPd materials and evaluated them as electrocatalysts for electrochemical CO2 reduction to formate.Although the materials were well characterized, the same concept has been reported in Angew.Chem., Int.Ed. (2021, 60, 21741-21745), where both intermetallic and solid-solution BiPd were prepared and demonstrated to efficiently covert CO2 into formate.Thus there is a big concern regarding the novelty.
Moreover, formate is a simple 2 electron transferred product during CO2 reduction and has been widely and efficiently generated over cheap tin, indium, and bismuth metals.It is unnecessary to add noble Pd, which largely increases the CO2RR catalyst cost and prevents them from practical application.
In the response letter, authors claimed that the anion exchange membrane is used when gaseous products dominate CO2 reduction, while the proton exchange membrane is employed for liquid product formation.This statement is not true and baseless.In fact, anion exchange membrane rather than proton exchange membrane is widely employed in CO2 electrolyzers.
As for formate crossover from cathode to anode, authors claimed a small amounts of formate (4-6% of catholyte) and a small carbon loss (~0.8-1%) but with a rather small current densities of below 30 mA cm-2 (compared to over 200 mA cm-2 required for industrial CO2 electrolysis) and within less than one hour electrolysis.How about over 100 hour electrolysis at an industrial relevant current density?Serious formate crossover and carbon loss will be very obvious in the current flow cell setup Therefore I can not recommend this study for publication in Nature Communications.
Reviewer #2 (Remarks to the Author): Accept as is.
Reviewer #3 (Remarks to the Author): The author has answered my question properly and I recommend publishing it on Nature Communications.

Dear reviewers,
We would like to thank you for the prompt and comprehensive review of our manuscript.
These insightful comments have greatly contributed to the improvement of our work.We have carefully studied the comments, supplemented additional experiments and provided a substantive discussion on the obtained results.Please find our detailed responses to each comment from the reviewer below, along with corresponding revisions highlighted in red text in the revised manuscript.
For reviewer #1: Comments Comments 3) In the response letter, authors claimed that the anion exchange membrane is used when gaseous products dominate CO2 reduction, while the proton exchange membrane is employed for liquid product formation.This statement is not true and baseless.In fact, anion exchange membrane rather than proton exchange membrane is widely employed in CO2 electrolyzers.As for formate crossover from cathode to anode, authors claimed a small amount of formate (4-6% of catholyte) and a small carbon loss (~0.8-1%) but with a rather small current densities of below 30 mA cm -2 (compared to over 200 mA cm -2 required for industrial CO2 electrolysis) and within less than one hour electrolysis.How about over 100 hours electrolysis at an industrial relevant current density?Serious formate crossover and carbon loss will be very obvious in the current flow cell setup.

Our response:
We greatly appreciate for the reviewer's insightful comment.The ion exchange membrane plays a key role in cell performance, and we totally agree with reviewer's opinion that the anion exchange membranes are currently widely employed under the most neutral or alkaline conditions.We sincerely apologize for our previously hasty and inadequate  [16][17][18][19][20] and resulting in highly concentrated liquid products collected in the cathode chamber, the challenge of product crossover persists.
Therefore, the claim of "a small amount of formate crossover (4-6 % of catholyte) and carbon loss (~0.8-1 %) below 30 mA cm -2 within one hour at -0.7V (vs RHE)" was indeed not rigorous at this stage.According to the reviewer's comment, we conducted a long-term constant current electrolysis at high current densities (100 mA cm -2 ) (Figure R1).The results clearly demonstrate a rapid decrease in formate Faradaic efficiencies and an increase in hydrogen production over 4 hours, accompanied by significant product crossover (~16 %) and carbon loss (~11 %), which have substantial implications for cell performance and cannot be overlooked any longer.This decline in performance is primarily attributed to electrode flooding, product crossover, carbon loss and salt accumulations resulting from physicochemical changes of the membrane and the gas diffusion layer during prolonged electrolysis at high current densities in alkaline media.It is worth noting that this product crossover and carbon loss will become more serious with the reaction time proceeding, if no treatment is carried out timely.
Thus, we have tried several strategies, including regular electrolyte refreshing, membrane replacement, and retreatment of the gas diffusion layer to mitigate this performance deterioration.Once a noticeable decrease in activity was observed after a certain period of electrolysis, we replaced the utilized electrolyte and membrane, as well as elaborately washing the cathode surface of the gas diffusion layer.After nearly a month of experimentation, as anticipated, this simple treatment resulted in a substantial reduction in operating voltage and an obvious recovery in formate Faradaic efficiencies (FEs), as depicted in Figure R2a.
Furthermore, through periodic treatments, the system exhibited superior stability for nearly 60 hours with small changes in formate crossover (~13 %) and carbon loss (~9 %), and a well-maintained formate selectivity (FE~70 %).These findings indicate that these treatments can effectively alleviate the product crossover and carbon loss to some extent during alkaline CO2RR.However, prolonged usage leads to gradual hydrophobicity loss of the gas diffusion layer, as evidenced by the decreasing contact angle (Figure R2b).Consequently, this hinders CO2 diffusion to reaction sites while promoting hydrogen evolution reaction and the electrode flooding at the reactive three-phase interface, thus limiting the further stability testing within the current flow cell setup.

For reviewer #2:
Comments: Accept as is.
Our response: We greatly appreciate for the reviewer's positive comment.

For reviewer #3:
Comments: The author has answered my question properly and I recommend publishing it on Nature Communications.

Our response:
We greatly appreciate for the reviewer's positive comment.The revised version has already been submitted online.
Thank you for your consideration!
Figure R1| a, XRD patterns b, SEM images c, FE and current density at -0.7V (vs.

Figure
Figure R2| a, XRD patterns b, SEM images c, FE and current density at -0.7V (vs.

Figure
Figure R3| a, XRD patterns b, SEM images c, FE and current density at -0.7V (vs.

Figure R8| a ,
Figure R8| a, Schematic of carbonate formation and crossover phenomenon observed using anion exchange membrane (AEM).b, Schematics of ion transport and reactions using proton exchange membrane (PEM).c, FE at -0.7V (vs.RHE) of the S1 and S6 using AEM and PEM.

Figure R9| a ,
Figure R9| a, Calibration curve used for estimation of formate concentration and b,

FigureFlow
Figure R10| a, IC curves and b, the formate concentrations (diluted 100 times) and Figure R11| a-b, Aberration-corrected HAADF-STEM images of S1 and S6 after

Figure R12|
Figure R12| XRD patterns of the S1-Bi 2 Pd products obtained at various reaction times.

Figure R13|
Figure R13| XRD patterns of the S4-Bi 2 Pd 5 products obtained at various reaction times.

Figure R14|
Figure R14| XRD patterns of the S6-BiPd 3 products obtained at various reaction times.

Figure R16|
Figure R16| XRD patterns of the S4-Bi 2 Pd 5 products using Pd(NO 3 ) 2 .2H 2 O as the Pd precursor obtained at various reaction times.

Figure
Figure R2| a, Long-term stability test of S1 at -100 mA cm -2 in flow cell.b, Contact angles of the cathode electrode surface at different reaction time and after treatment.
To date, although various IMCs such as Bi-Pb 18 , Bi-Mo 19 , Bi-Ni 20 have been successfully prepared, a controllable synthesis of a Bi-based intermetallics family with tunable Comments 1)The reports about BiPd intermetallics are shown below:(https://doi.org/10.1016/S1872-2067(21)63999-2;https://doi.org/10.1002/anie.202109288;https://doi.org/10.31635/ccschem.022.202202357 ) Our response: We thank for the reviewer's useful comment.Bi-based bimetallic catalysts are emerging as fascinating materials with remarkable catalytic properties.Intermetallics provide a desirable platform for atomic-scale structural design and in-depth understanding of the structure-performance correlations in catalyst materials.As perfect catalyst candidates, if a Bi-based intermetallics family with tunable composition and atomic arrangement could be achieved, it is definitely of great significance for a systematic and deeper understanding of the structure-activity correlation for specific catalytic reaction due to their special surface properties and well-defined atomic arrangements.However, a controllable synthesis of a Bibased intermetallics family is barely investigated because it is a huge challenge to develop a facile method to fine tune the atomic-level surface structure and the compositional stoichiometry of IMCs.In literatures, the intermetallic PdBi nanosheets (https://doi.org/10.1016/S1872-2067(21)63999-2)andPd3Biorderednanocrystals(https://doi.org/10.1002/anie.202109288)havebeenreported;however,from the point view of synthesis, an extremely complicated multiple-steps template-assisted method was involved for synthesis of PdBi nanosheets, and a general solvothermal process followed by a high temperature annealing treatment (500 ℃) was employed for Pd3Bi intermetallic preparation.In respect of catalytic performance, both works focused on catalytic property comparison between fully ordered Pd-Bi products with corresponding disordered ones and gained a similar conclusion that intermetallic products exhibited excellent formate selectivity.The review paper mentioned by this reviewer summarized a synthesis of variousBi-basedbimetallic catalysts, which included Pd3Bi intermetallic and other bimetallic products (e.g.Bi-Sn, Bi-Cu).Generally speaking, few studies have been implemented to synthesize a family ofBi-PdIMCs with tunable composition and atomic arrangement via a simple and general wet chemical route because it is difficult to achieve the synthesis of multiple IMCs with different structures under the same synthesis system.Likewise, it also lacks a systematic and deeper understanding of the structure-activity correlation for intermetallic families with different compositions for specific catalytic reaction.Therefore, the development of a simple and general system for the controlled synthesis of ordered IMCs still remains a huge challenge.In this work, we successfully fabricated up to six Bi-Pd ordered IMCs, including Bi2Pd, BiPd, Bi3Pd5, Bi2Pd5, Bi3Pd8 and BiPd3 via a EG co-reduction solvothermal method for the first time.A combination of XRD, AC-STEM, XAS and Atomic resolution EDX mapping were used to delicately confirm the structure of Bi-Pd IMCs family.Moreover, using electrocatalytic CO2 reduction as a model reaction, we systematically investigated the catalytic properties of Bi-PdIMCs and corelated their particular performances with unique surface structure of each product.The unique full understanding of the specific structure-performance relationship of the IMCs in this work provides a valuable paradigm for precisely modulating the structure of catalyst materials.Therefore, we believe that this work can provide some new insights for the controlled synthesis of IMCs and the selective regulation of catalytic intermediates by different ordered structures.It is the first example for controllable synthesis of six different ordered Bi-"Bi-based bimetallic catalysts are emerging as fascinating materials with remarkable catalytic properties.As perfect catalyst candidates, if a Bi-based intermetallics family with tunable composition and atomic arrangement could be achieved, it is definitely of great significance for a systematic and deeper understanding of the structure-activity correlation for specific catalytic reaction due to their special surface properties and well-defined atomic arrangements.Comments 2) Usually, restructuring of the metal catalysts occurs during electrochemical CO2RR occurs.Thus, the real active site may not be BiPd intermetallics at all.Is that possible that the authors perform in-situ examination of XAS, XRD or perform such characterization for the spent samples.Our response: We thank for the reviewer's useful comment.The restructuring phenomenon usually occurs during electrochemical CO2RR of metal catalysts which have been widely studied in literatures [J.Am.Chem.Soc.2023, 145, 18, 10116; ACS Nano 2019, 13, 9, 10818-10825].Interestingly, most studies focused on unstable catalyst under the electrochemical environment.As a perfect candidate to study the structure-activity correlations in catalytic processes, another overwhelming advantage of intermetallics is their extremely stable properties during electrocatalysis, which have been well demonstrated in lots of studies [Nat.lack of fine surface information obtained from XRD, we further employed HAADF-STEM to study the surface structure of post-electrocatalyst from an atomic level.Taking Bi2Pd (S1) and BiPd3 (S6) as examples, which represent the highest formate and CO efficiently convert CO2 to formate in recent years [J.Am.Chem.Soc.2021,143, 14, 5386; Angew.Chem.Int.Ed.2021, 60, 38, 20627].In this work, we mainly focus on the synthesis of various Bi-Pd intermetallics via a facile solvothermal method.As ideal catalyst candidates, we then investigate structure-performance relationship over various Bi-In turn, when indissoluble palladium acetylacetonate is used, the nucleation is slower.No reduction product was formed in the first 1 h.A very limited solubility of Pd(acac)2 also restricted the reduction rate of Pd(II) ions, which extended the growth period of Pd to 12 h.
We thank for the reviewer's useful comment.Formate product has been widely reported over diverse electrocatalysts in literatures, while they have not been generally demonstrated outside laboratories.The current market price and operating cost have strongly suggested that formate is the most commercially available product.Therefore, there is a growing impetus to process due to the intrinsic adsorption properties of synthesized six Bi-Pd IMCs.Specifically, Bi2Pd displays an excellent high formate selectivity.The insights gained from this work not only shed light on the synthesis of intermetallic nanocrystals via a facile solvothermal method but also provide an important knowledge framework that guides the rational design of architecturally sophisticated multimetallic nanostructures toward optimization of catalytic molecular transformations during heterogenous catalysis.Comments 4) However, it remains a huge challenge in the controllable synthesis of IMCs, as diffusing a metal atom into a lattice of another metal to form a regular metal occupancy is no picnic.The formation mechanism for the intermetallic is not well supported by data.Can the authors monitor the formation dynamics for such intermetallics?Why do you have to change the type of Pd precursors to regulate the ratio of Pd to Bi in the intermetallics, but just using only one single Pd precursors.and the type of Pd precursors.It is not an easy endeavor to monitor the formation dynamics for such intermetallics, which requires advanced techniques such as operando XAFS and in situ HAADF-STEM during solvothermal process.According to the reviewer's suggestions, we tried to monitor and analyze the growth process of Bi-Pd IMCs by powder X-ray diffraction.demonstrated a reversible phase transformation, which always co-existed even further prolonging the reaction time, probably due a comparable thermal dynamic stability.For Bi2Pd5 synthesis, beside Pd formation, a simultaneous generation of BiOCl product was also observed within the initial 5 h reaction due to the introduction of chlorine-containing Pd precursor (sodium tetrachloropalladate, Na2PdCl4).As the reaction proceeded, BiOCl was sequentially reduced into Bi, which then experienced atomic interdiffusion with Pd under solvothermal alloying conditions, leading to the formation of BiPd3 intermetallic after 6 h reaction.As more Bi generation and diffusion, BiPd3 gradually converted into stable Bi2Pd5 intermetallic product after 8 h reaction.Slightly different with Bi2Pd and Bi2Pd5, the formation of BiPd3 looks more straightforward.Both Pd and BiPd3 phase appeared in the first 1 h reaction, which then underwent a further Bi deposition and atomic diffusion to generate a may be explained by their solubility in reaction solvent.For example, when more soluble Pd(NO3)2 is used, the release rate of Pd 2+ is fast, resulting in a quick nucleation of BiPd3/and Pd with 1h.However, when a weak solubility palladium acetate was used, the release rate became slow, and only Pd and some organic impurities appeared at 1h. temperature, Bi/Pd molar ratio, and the type of Pd precursors (Supplementary Figs.S1

1 )
Authors prepared intermetallic BiPd materials and evaluated them as electrocatalysts for electrochemical CO2 reduction to formate.Although the materials were well characterized, the same concept has been reported in Angew.Chem., Int.Ed. (2021, 60, 21741-21745), where both intermetallic and solid-solution BiPd were prepared and demonstrated to efficiently covert CO2 into formate.Thus, there is a big concern regarding the novelty.
[8][9][10][11][12][13][14] for the reviewer's concerns and totally agree with the reviewer's opinion that efficient conversion of CO2 to formate has been achieved over certain metals, such as Sn, In, and Bi[8][9][10][11][12][13][14].If only the market price and practical application are considered, as a model reaction, we systematically investigated and compared the catalytic properties of six Bi-Pd IMCs, revealing distinct selectivity towards C1 products on these samples.While hexagonal BiPd exhibits high selectivity for formate (FE>80 %), orthorhombic BiPd3 15e migration of liquid products through the membrane, driven by electroosmotic drag or diffusion due to concentration gradients, can result in their dilution in the anodic stream, thereby increasing the separation cost, or their oxidation back to CO2, leading to decreased device efficiency15.To date, there are numerous studies specifically addressing these issues using a solid electrolyte reactor, strong acid electrolyte or employing bipolar membranes[Wang et al., Nature Catalysis, 2022, 5, 288-299; Edward H. Sargent et   al., Science, 2021, 372, 1074-1078; David Sinton et al., Joule, 2022, 6, 1333-1343].Despite these advancements have been made in CO2 electroreduction membrane is used for CO production over 2H/fcc-Heterophase AuCu Nanostructures[Zhang   et al., Advanced Materials, 2023, 35, 2304414].We also fully agree with reviewer's viewpoint that the utilization of anion exchange membranes is inevitably accompanied by product crossover or carbon loss.